A Molecular Evolutionary Clock for Angiosperms

Summary Pairs of angiosperm species putatively separated by continental drift following the break‐up of Gondwanaland have been used to derive linear regressions relating macromolecular differences to time. Differences have been derived from N‐terminal amino acid sequences of the small subunit of rubisco from members of Proteaceae, Winteraceae, Nothofagus and Solarium. Alternative sets of times have been taken from the literature on plate tectonics and biogeography. Botanical criteria have been used to discriminate tentatively between the two regression lines. The rate of evolution corresponding to the preferred regression is one inferred nucleotide difference between two evolutionary lineages in seven million years. An estimate of the variance about the regression lines has been obtained and has allowed suggestions about which species disjunctions are likely to have originated more recently than the continental separations.